The objectives of this proposal are: 1) to develop techniques for detecting the mutagenic potential to mammalian cells of chemicals, particularly those requiring metabolic activation; 2) to elucidate the factors involved in the sensitivity of mammalian cells to mutagenesis such as cell cycle effects; and 3) to evaluate mutagenic hazards of specific environmental chemicals such as pesticides. Non-dividing metabolically active primary rat liver cells will be co-cultured as metabolizing feeder cells with various target human cell lines as an assay for mutagenesis. The extent of mutation to purine analog- or ouabain-resistant mutants will be quantified. Synchronized human target cells will then be used in the assay so that the extent of mutation can be related to the degree of DNA synthesis. The interaction of the mutagens with DNA will be studied and attempts will be made to relate the extent of mutation to critical interactions of the mutagens with DNA. Finally, the most sensitive assay conditions will be employed to evaluate the mutagenic potential of several organochlorine pesticides.